Heat Loss - block basement

[Homeowner314]

In the Lansing, MI area, 0°F design temp, ~50°F deep ground temp, 7000 heating degree days, approximately what would be the design BTU loss from a standard block basement, 30' x 40' x 8', with 6' buried and 2' exposed, and zero insulation, 60°F interior temp?

What would I save if I put R-6.5 foam on the upper 4' of the exterior (2' buried, 2' exposed)?

[NCHeat]

minimal. By my half a$$ load calc (knowing almost nothing about the rest of the house) with no insulation on walls and at least r-38 in the houses roof the loss in about 11K, With r-5 on the basement walls it drops the loss to about 9K.

[Homeowner314]

Thanks. I was hoping my calcs were off, I was getting 15-20k for the basement.

What about the above ground part of the basement with zero degree air on the other side?
60° Td, 280 square feet, isn't hollow 8" block about R-2?
When I ran that bit of wall through an online calculator it gave me 8400 for just that exposed part, which really got my attention.

I'll be thrilled if I was wrong, of course.

I just realized one mistake I made. The BTUs coming through my R-4 floor are a loss to the house, but a source of heat to the basement, so they cancel out, right?

Here's the whole thing:

The basement specs are in the OP.
House is a 30x40x8' ranch, R19 ceiling, R11 walls.
155 square feet of 1994 vintage triple pane (clear uncoated glass), maybe 1/4" between panes.
42 square feet of 1970s vintage aluminum framed sliding patio door.
3 insulated steel doors. I ignored the doors, assuming their R-value was about the same as the wall.

Infiltration is my big unknown variable, can I assume one exchange per hour for something made in the late 1970s with blown cellulose, that got new windows and vinyl siding in 1994?
The siding appears to be cellotex, covered by 1/8" of foam, then the vinyl.

Is the whole house going to be under 40k as-is, or easily improved to sub-40k? (zero degree design temp)
My idea of easy is blowing another R20-R30 into the ceiling, covering the above grade foundation, etc.

[beenthere]

minimal. By my half a$$ load calc (knowing almost nothing about the rest of the house) with no insulation on walls and at least r-38 in the houses roof the loss in about 11K, With r-5 on the basement walls it drops the loss to about 9K.

He's asking about a basement. So the house roof has no bearing.

[Homeowner314]

He's asking about a basement. So the house roof has no bearing.

So, does the basement lose about 11k, or not? :bump:

If anybody wants to take a shot at the whole house, I forgot to mention that 6x7 sliding patio door is double pane, clear glass.

[skippedover]

Are you actually asking us to do a full load calculation of your house at no charge? That is a job for the installing contractor, not an on-line help group. Suffice it to say, don't use any contractor who fails to do a room-by-room load calculation. End of story in my book.

[NCHeat]

He's asking about a basement. So the house roof has no bearing.

What if its a basement without a house on top of it ?????????

I think the rest of the house has bearing on this

[Homeowner314]

Are you actually asking us to do a full load calculation of your house at no charge?

If somebody is generous enough to do a full calc, that would be wonderful.

But what I really need is some idea of the basement heat loss, one guy says 11k, which sounds reasonable, but then there's disagreement amongst pros over whether I gave enough info to calc the basement.

What I've got outside of this forum is two pros saying 1200 sq ft needs a 60-70k furnace. I think that both of them are saying 45k is too small, a 90k is too big, so don't waste time calculating anything, just stick a 70k in the house.

Everything I can calculate says I've on the edge of being able to do it with a furnace that's rated for 39k output. I'd really like to go with the smaller one for longer run times, less electricity for the blower, and especially less upgrade work on my duct system. OTOH, if the house drops to 65°F on a cold night with the furnace running 100%, I won't be happy with that. If somebody can confirm that I might be in the ballpark, I'll probably go ahead with the 39k output and plan on upgrading the house if the furnace struggles.

[NCHeat]

If somebody is generous enough to do a full calc, that would be wonderful.

But what I really need is some idea of the basement heat loss, one guy says 11k, which sounds reasonable, but then there's disagreement amongst pros over whether I gave enough info to calc the basement.

What I've got outside of this forum is two pros saying 1200 sq ft needs a 60-70k furnace. I think that both of them are saying 45k is too small, a 90k is too big, so don't waste time calculating anything, just stick a 70k in the house.

Everything I can calculate says I've on the edge of being able to do it with a furnace that's rated for 39k output. I'd really like to go with the smaller one for longer run times, less electricity for the blower, and especially less upgrade work on my duct system. OTOH, if the house drops to 65°F on a cold night with the furnace running 100%, I won't be happy with that. If somebody can confirm that I might be in the ballpark, I'll probably go ahead with the 39k output and plan on upgrading the house if the furnace struggles.

I would be concerned that both contractors "think" 45K is too small. Neither one of them knows. You don't have to guess at this. Have one of them do a full room by room Manual J calc.

[hvacvegas]

What if its a basement without a house on top of it ?????????

I think the rest of the house has bearing on this

If there wasn't a conditioned space above it, then it would matter.

But, there is. Kinda like interior rooms on the first floor (in a 2 story) have no load.

[beenthere]

What if its a basement without a house on top of it ?????????

I think the rest of the house has bearing on this

Since the OP has a house on top of his basement. The roof of the house doesn't count.